1. Field of the Invention
This invention is related to the field of voltage regulators, and particularly to a voltage regulator employed within a phase locked loop (PLL).
2. Description of the Related Art
Voltage regulators are used in a variety of systems to provide a regulated voltage to other circuits in the system. Generally, it is desirable to provide a stable regulated voltage in the face of a wide variety of loads, operating frequencies, etc.
A measure of the effectiveness of a voltage regulator is its power supply rejection ratio (PSRR), which measures the amount of noise present on the power supply to the voltage regulator which is transmitted to the regulated voltage. A high PSRR is indicative of a low amount of transmission of noise, and a low PSRR is indicative of a high amount of noise transmission. A high PSRR, particularly across a wide range of operating frequencies of the devices being supplied by the voltage regulator, is difficult to achieve.
For example, voltage regulators have been used in the past to power PLL circuitry. However, PSRRs of voltage regulators used in PLLs have been limited. For example, PSRRs greater than 25 dB may not been achieved in voltage regulators used in PLLs.